1. Field of the Invention
The present invention relates generally to an improvement in the detection and measurement of images or pictures in a film, such as an X-ray picture film, by illuminating the X-ray picture film with light. More particularly, it relates to a measurement of bones, especially human bones, by using an X-ray film having radiographical pictures of sample bones therein, for obtaining from an X-ray picture film various data, i.e., medical data. The present invention further relates to an improved method of and apparatus for measuring bone data such as morphometric data of bones, bone density data, and bone mineral content data by using a radiographical picture of bones in an X-ray picture film.
2. Description of the Related Art
A radiographical measurement of bones including bone morphometry is performed to evaluate the growth and aging of human bones, the diagnosis and confirmation of the rate of progress of bone diseases such as osteoporosis and osteomalacia, and the confirmation of the effect of treatments applied to various bone diseases.
The typical conventional methods for bone measurement are the microdensitometry (MD) method, and the photon-absorptiometry method. The former method measures the tone of the X-ray picture film of sample bones by a microdensitometer for bone measurement, and the latter method detects and measures the quantity of gamma rays, transmitting through sample bones, for bone measurement.
The MD method has become widely used because the method uses readily available X-ray picture film which can be easily obtained by an X-ray camera used widely for diagnosing bone fractures.
The photon absorptiometry method has, however, a drawback in that the use of the gamma-ray generator has not become as wide-spread as that of the X-ray camera.
Nevertheless, the above-mentioned microdensitometric bone measurement requires many manual work steps as described hereinbelow. Namely, when conducting conventional microdensitometric bone measurement or bone morphometry, a reference point for the bone morphometry is determined in the X-ray film of sample bones. Subsequently, an object region, such as a region on a line crossing the middle point of the longitudinal axis of the second metacarpal bone, is selectively measured by a predetermined procedure with reference to the reference point. The examined region is subsequently scanned by a microdensitometer so as to measure the intensity of light transmitting through the examined region, and the measured intensity of light transmitting through the region or the measured quantity of light absorbed by the region is recorded as a diagram on a chart. On the other hand, the X-ray radiography of a standard aluminum step block (it is hereinafter referred to as an aluminum step wedge), taken together with the X-ray radiography of the sample bones is scanned along its longitudinal axis by the microdensitometer, and the measured quantity of light transmitting through or absorbed by the aluminum standard step wedge is recorded as a different diagram on a chart. The diagram of the quantity of absorbed light is then converted by a digitizer into digital data to be inputted into an electronic computer to thereby convert the quantities of absorbed light at a plurality of points on the sample bones into corresponding gradations of the aluminum standard step block. The electronic computer then calculates and outputs various indices representing the bone morphology of the examined region on the basis of a pattern expressed by the gradations of the aluminum standard step wedge.
With the above-mentioned conventional MD method, the tone of the picture of the X-ray picture film of the sample bones is greatly dependent on both radiographying condition and developing condition to obtain the film, and the measurement of the X-ray picture film of the sample bone is impossible or, even if the X-ray picture film can be measured, the measured result includes large errors.
Further, when the pictures of the X-ray picture film are measured, an LED light source is often used for illuminating the X-ray picture film, and the light emitted by the LED light source and transmitting through or reflected from the film is usually detected by a CCD image sensor light detecting means. Nevertheless, the CCD image sensor is often adversely affected by the thermal conditions around the CCD image sensor. Namely, with an increase in temperature, the electric output, i.e., the voltage output delivered by the CCD image sensor subject to no input light increases as shown in FIG. 8. The voltage of the CCD image sensor under no-light conditions will be referred to as "an electric shielded output voltage" throughout the description of the specification, the accompanying claims, and the drawings of the present patent application. Since the electric shielded output voltage of the CCD image sensor is always superposed on an actual detecting output voltage of the CCD image sensor, such electric shielded output voltage brings about an error in the detecting and measuring operation of the CCD image sensor. Thus, it is important to provide an appropriate means for compensating for the electric shielded output voltage of the CCD image sensor during the measuring operation thereof.